Current electric appliances demonstrate a tendency to have a reduced weight and a smaller size, which leads to development of electrochemical devices, such as lithium ion secondary batteries, having a high energy density. Further, electrochemical devices such as lithium ion secondary batteries are used in more various fields, and thus are desired to have improved characteristics. In particular, improvement of battery characteristics of lithium ion secondary batteries will become a more and more important factor when the batteries are put in use for automobiles.
Patent Literature 1 discloses use of lithium-bis(oxalato)borate and Li[(C2O4)2B] as conductive salts in lithium ion batteries.
Patent Literature 2 discloses an electrolyte for electrochemical devices including a compound having a specific chemical structural formula and at least one selected from the group consisting of compounds represented by Aa+(PF6−)a, Aa+(ClO4−)a, Aa+(BF4−)a, Aa+(AsF6−)a, or Aa+(SbF6−)a. The examples of this literature discloses an electrolytic solution containing 0.05 mol/l of a lithium borate derivative having a structure represented by the following formula:
and 0.95 mol/l of LiPF6 dissolved in a solvent mixture consisting of 50 vol % ethylene carbonate and 50 vol % dimethyl carbonate.
Patent Literature 3 discloses an electrolytic solution including a solvent containing a carbonate ester derivative having a halogen atom, a first anion represented by the formula:[B(CiH2(i-2)O4)(CjH2(j-2)O4)]−(wherein i and j are each an integer of 2 or greater), and a second anion other than the first anion.